This invention relates to the preservation of objects that contain cellulose-type materials, in particular, to a product, in the form of a solution, for de-acidification of cellulose-type materials composed of carbonated magnesium di-n-propylate, n-propanol and a hydrofluorocarbon diluent.
There is a lot of concern for the deterioration undergone by cellulose-type materials (books, documents, maps, press, magazines and tissues) held in libraries, newspaper archives, museums and archives. This deterioration endangers the physical integrity of many documents, books and tissues and thus forces a restriction in access and handling thereof. The most significant cause of deterioration in cellulose-type materials is hydrolysis catalyzed by acids in the cellulose, giving rise to a shortening of the polymeric chains of the cellulose, which, in turn, leads to a weakening of the cellulose fibers and they become more fragile. Many factors contribute to the acidification of cellulose-type materials. For example, acidic gases present in contaminated air, the use of alum and colophony (abietic acid) in paper production, products for oxidative degradation of cellulose, inks and other substances that oxidize cellulose which are present in paper and books.
A great deal of effort has been put in to the development of processes to achieve de-acidification of cellulose-type materials and thus to prolong their useful life by stopping acidic hydrolysis degradation processes. Specific compositions and products have been studied for de-acidification, capable of neutralizing the acid present in cellulose-type materials and introducing an alkaline reserve, which inhibits re-acidification. Technology has moved on from expensive craft methods using aqueous medium to the development of methods for applying alkaline reagents, dissolved in non-aqueous vehicles, either in liquid or solid state, to prevent books from falling apart.
The North American patent U.S. Pat. No. 3,676,182 (R. D. Smith, 11th Jul. 1972) relates to a procedure for non-aqueous de-acidification of paper using magnesium methoxide, dissolved in methanol to a concentration lying between 5% and 11%, as the de-acidifying agent. The resulting solution can be diluted with a chlorofluorocarbon (CFC) diluent, such as trichlorofluoromethane or dichlorodifluoromethane, until a liquid is formed, under pressure, that contains between 1% and 2% of the de-acidifying agent. The CFC compound quickly evaporates from paper impregnated with the de-acidifying solution containing methanol, thus minimizing the solvent effect of methanol on certain inks. The books and papers can be treated by immersion in the de-acidifying solution, or the solution can be applied with a brush or using a spray. Nevertheless, this method is not free from drawbacks as the magnesium methoxide is extremely sensitive to water. So much so that even traces of moisture lead to immediate hydrolysis forming a gelatinous precipitate of magnesium hydroxide. This is insoluble in water and many organic solvents. Unless the paper has been sufficiently desiccated before treatment premature hydrolysis of the magnesium methoxide may occur, leading to the formation of unwanted white marks of powdered magnesium hydroxide on the surface of the paper, giving the paper a rough feel. On the other hand, the spray nozzles frequently become blocked and the brush bristles become caked, making it necessary to clean them and then dry them thoroughly before using them again.
The North American Patent U.S. Pat. No. 3,939,091 (Kelly, G. B., 7th Feb. 1976) discloses and claims a product for the de-acidification of paper that overcomes the problems of previous de-acidification solutions based on magnesium methoxide dissolved in CFC. The magnesium methoxide dissolved in methanol or in a methanol and trichlorotrifluoroethane (Freon(copyright) F7) mixture is reacted with gaseous carbon dioxide to obtained a colourless 20% solution of methoxymagnesium methylcarbonate. The resulting solution is more tolerant of water than the magnesium methoxide solutions, and obstructions are not produced in the spray nozzles as often as before.
The Canadian patent CA 1.147.510 (Smith, R. D., 7th of Jun. 1983) discloses a method for the production of methoxymagnesium methylcarbonate. Metallic magnesium is allowed to completely react with methanol to form magnesium methoxide. This is then re-dissolved in methanol saturated with carbon dioxide forming a methoxymagnesium methycarbonate solution. This solution is diluted with trichlorotrifluoro-ethane or with dichlorodifluoromethane. The diluted solution is sprayed onto the paper to be de-acidified. As an alternative, the paper can be submerged in the same solution, with the liquid state being maintained under pressure.
The North American patent U.S. Pat. No. 4,860,685 (Smith, R. D., 29th of Aug. 1989) and the corresponding Canadian patent CA 1.272.018 (31st of Jul. 1990) describe a flexible spraying system for the de-acidification of cellulose-type materials. A de-acidifying agent, preferable an alkoxide of magnesium carbonate, is combined with a CFC diluent, preferably trichlorotrifluoroethane, and with a propellant gas, preferably dichlorodifluoromethane. Additional pressurization and propulsion can be achieved using an inert gas such as nitrogen. The carbonated magnesium alkoxide, such as methoxymagnesium methylcarbonate or ethoxymagnesium ethylcarbonate, is produced by dissolving the corresponding magnesium alkoxide in alcohol in the presence of carbon dioxide.
The procedures described above use CFCs as these are essentially non-reactive and so do not imply a direct toxic risk for living beings. However, these same properties of chemical inertness that the CFCs possess make them problematic in the stratosphere. It has been demonstrated that the CFCs are the main factor responsible for the destruction of the stratospheric ozone layer and that they contribute to the greenhouse effect in the troposphere. The problem revolves around the chlorine that is liberated when the CFCs are exposed to ultraviolet radiation and other more penetrating radiations in the stratosphere. The chlorine destroys ozone by catalysing its transformation into molecular oxygen. The production of CFCs has been banned since the 1st of Jan. 1996 (Copenhagen Agreement which amends the Montreal Protocol of the 23-25th of Nov. 1992), and use thereof should be totally eliminated before the year 2030.
The Canadian patent CA 2.142.195 (Worsford, D. James, 8th of Feb. 1995) discloses and claims a product for de-acidification of cellulose-type materials which consists of a de-acidifying reagent, such as methoxymagnesium methylcarbonate or ethoxymagnesium ethylcarbonate, a solvent such as methanol or ethanol, and a hydrochlorofluorocarbon diluent (HCFC) or hydrofluorocarbon (HFC). The product patented can be applied to the cellulose-type material by spray or with a brush, or by immersing the cellulose-type material in the product. As a novelty with respect to the patents cited earlier this patent describes the use of diluents that are not prohibited by the Montreal Protocol [HCFCs and HFCs].
The use of HCFCs and HFCs as a substitute for CFCs substantially reduces the number of chlorine radicals that can be liberated in the stratosphere on exposure to cosmic radiation, thus reducing the potential for ozone destruction. On the other hand, the presence of hydrogen means that the compound is more reactive, such that it tends to decompose more easily before reaching the stratosphere. The rate of decomposition of HCFCs and HFCs is higher than that of the CFCs, whose lifetime is quoted at being between 60 and 100 years.
The object of the present invention is to find a new product for the non-aqueous de-acidification of cellulose-type materials, thus providing an addition to the arsenal of means available for combating acidification of cellulose-type materials.
Therefore, an object of this invention consists of a product, in the form of a solution, for the non-aqueous de-acidification of cellulose-type materials which comprises carbonated magnesium di-n-propylate, n-propanol and an HFC diluent.
An additional object of this invention consists of a procedure for production of said product for the de-acidification of cellulose-type material.
Another additional object of this invention consists of a method for de-acidification of cellulose-type material which comprises use of the aforementioned product.
The present invention provides a product for de-acidification of cellulose-type material, hereinafter denominated the product of the invention, characterized because it is presented in the form of a solution and is comprised of:
carbonated magnesium di-n-propylate,
n-propanol, and
an HFC diluent selected from 1,1,1,2-tetrafluoroethane (HFC 134a) y 1,1,1,2,3,3,3-heptafluoropropane (HFC 227).
Carbonated magnesium di-n-propylate is a white solid, with the formula (CH3CH2CH2O)2 MgOCO, soluble in anhydrous n-propanol and in medium-polarity solvents, such as HFC 227 and HFC 134a, whose polarities are 0.8 Debyes (D). The meaning of the term xe2x80x9corganic solvents of medium polarityxe2x80x9d in this description includes solvents with a dipole moment (xcexc) less than water [:1.8 D], for example, toluene [:0.40 D] and n-propanol [:1.5 D]. Carbonated magnesium di-n-propylate has a dipole moment of 0.8 D and so, in general, it is soluble in any proportion in the HFC diluent used for producing the product of the invention. The dipole moment of this diluent is approximately 0.9 D. Carbonated magnesium di-n-propylate, on coming into contact with moist air, reacts to give magnesium/carbonate and magnesium hydroxide, and slowly releases n-propanol according to the reaction [1]:
2(CH3CH2CH2O)2MgOCO+3H2O_Mg(OH)2+MgCO3+4CH3CH2CH2OHxe2x80x83xe2x80x83[1]
Carbonated magnesium di-n-propylate reacts vigorously with mineral acids releasing carbon dioxide and n-propanol, forming soluble magnesium salts as indicated by reaction [2]:
(CH3CH2CH2O)2MgOCO+2HCl_MgCl2+CO2+2CH3CH2CH2OHxe2x80x83xe2x80x83[2]
As a result of the high solubility of carbonated magnesium di-n-propylate in polar solvents, characterized by low surface tension and viscosity values, it can be dispersed deeply through the pores in the paper, reaching all points of cellulose-type material, and neutralizing the acids present. The excess reagent slowly decomposes into magnesium carbonate hydroxide, a stable compound of the formula (MgCO3)4.Mg(OH)2.5H2O, which it deposited among the paper fibres to act as a alkaline reservoir protecting against acidic atmospheric contaminants and acids released in the paper during ageing. The trials carried out on papers treated and submitted to accelerated ageing have shown that treatment with the product of the invention [see Example 3] stabilizes the properties of the mechanical resistance of the paper, manifesting itself as a stabilization in the degree of whiteness.
Carbonated magnesium di-n-propylate can be obtained from magnesium di-n-propylate by a procedure that comprises the stages of:
reacting a suspension of magnesium di-n-propylate in n-propanol with gaseous anhydrous carbon dioxide, until a solution of carbonated magnesium di-n-propylate is obtained; and
separating said solution of carbonated magnesium di-n-propylate in n-propanol from the residual products, for example by decantation.
Reaction of magnesium di-n-propylate with anhydrous carbon dioxide is an exothermic reaction, reaching temperatures of up to 45xc2x0 C. and the initial solid compound insoluble in n-propanol [magnesium di-n-propylate] is transformed into a soluble form consisting of carbonated magnesium di-n-propylate. The reaction is taken to have reached its conclusion when the temperature drops to room temperature. Next, the dark solid insoluble particles are allowed to sediment out on the bottom of the recipient and to give a clear and transparent solution. The resulting solution is collected by conventional techniques, for example, by decantation or, preferably, by suction under vacuum, and transferred to recipients suitable for loading, dilution or dosing. The carbonated magnesium di-n-propylate obtained is purified, for example, by evaporation of part of the solvent (typically 20-30%) under vacuum.
The concentration of carbonated magnesium di-n-propylate in the alcoholic solution lies between 30 and 70% (P/P), preferably between 45 and 50% (P/P) of carbonated magnesium di-n-propylate, the rest consisting of n-propanol. It can be adjusted to the desired concentration by conventional methods, for example, by dilution with n-propanol or by elimination of excess solvent.
Magnesium alkoxides can be obtained using known methods for example, Metal Alkoxides, by Bradley, D. C., Mehrotra, R. C. and Gaur, D. P., Academic Press, London (1978), and the work of Thoms, H., Epple, M., Viebrock, H. and Reller, A., J. Mater. Chem. 5(4)589, (1995), where the synthesis of different magnesium alkoxides from alcohols of up to four carbon atoms is described. Although various magnesium alkoxides are known, the literature only describes carbonated magnesium alkoxides derived from methanol (methoxymagnesium methylcarbonate) and ethanol (ethoxymagnesium ethylcarbonate) and the carbonate of methoxy and butoxy polyethylene glycol [WO 90/03466].
The suspension of magnesium di-n-propylate in n-propanol can be prepared by different procedures. One of them (Procedure A) comprises reacting magnesium metal with anhydrous n-propanol, in the presence of iodine, at the temperature corresponding to the boiling point of the mixture. Another procedure (Procedure B) comprises reacting magnesium metal with anhydrous n-propanol in the presence of iodine at reflux temperature and the addition of toluene to form an azeotrope with n-propanol. The magnesium metal used in either Procedure A or B may in the form of a strip, in which case, it requires a suitable preparation (see Example 1.2).
Alternatively, the suspension of magnesium di-n-propylate in n-propanol can be prepared by a procedure (Procedure C) which does not require the use of a strip of magnesium but rather magnesium in powder form, with a granulometric distribution between 50 and 150 m. This procedure C therefore comprises of; (i) reacting magnesium in powder form, with a granulometric distribution between 50 and 150 m, with anhydrous n-propanol in the presence of iodine, which acts as a catalyst. The mixture is gently heated until hydrogen begins to be released. From this moment on, as the reaction is strongly exothermic, the next step (ii) consists of cooling the reaction mixture to the temperature corresponding to the boiling point, with a view to controlling the reaction rate with gentle boiling until hydrogen is no longer given off and the last remaining particles of magnesium have disappeared. In this fashion a suspension of magnesium di-n-propylate in n-propanol is obtained.
The use of magnesium in the form of powder with the indicated granulometric distribution (50-150 m) means that the reaction of magnesium with n-propanol in the presence of iodine is exothermic, and so the reaction medium should be cooled instead of additional energy being provided. This also allows the reaction time to be reduced [typically, the total reaction time for production of magnesium di-n-propylate is 4-5 hours].
Carbonated magnesium di-n-propylate can be used in the production of a product, in the form of a solution, suitable for de-acidification of cellulose-type material along with n-propanol, and a diluent selected from HFC 134a and HFC 227.
The meaning of xe2x80x9ccellulose-type materialxe2x80x9d as used in this description refers to a material totally or partially composed of cellulose fibres, including paper of all classes, tissues and fabrics which contain cellulose fibres of vegetal origin, for example, those produced from wood, cotton, flax, jute, hemp and other plants. Examples of such cellulose-type materials include books, documents, maps, works of art, articles elaborated with said materials, clothing, flags, etc.
For use as a reagent for de-acidification of cellulose-type material a solution of carbonated magnesium di-n-propylate and n-propanol is produced, in HFC diluent, at a concentration lying between 30% and 70% (W/V) for application by machine and of 3.5% to 4.5% (W/V) in said HFC diluent for application by sprays. In general, said solution is of light chestnut colour and viscous. To reduce as much as possible the unwanted effects of the alcohol on the components of the paper, it is useful to concentrate the resulting solution as much as possible while maintaining a suitable fluidity for dosing.
The concentrated solution of carbonated magnesium di-n-propylate is diluted to the desired concentration with a chemically inert and non-toxic diluent which allows the de-acidifying reagent to be carried inside the cellulose-type material. An HFC selected from HFC 134a and HFC 227 can be used as diluent. HFC 227 is preferable. HFC 227 has a boiling point of xe2x88x9217.3xc2x0 C. at normal pressure (101.3 kPa), a liquid density of 1.417 g/cm3 at 20xc2x0 C. (399.3 kPa). The surface tensions are 9.31 mN/m (at 0xc2x0 C.), 6.96 mN/m (at 20xc2x0 C.) and 4.8 mN/m (at 40xc2x0 C.) and its dipole moment is 0.2xc2x10.14 D. HFC 227 has been marketed since 1991 as a substitute for R12 and R114 in sectors where these chemicals have been used as coolants. The company SOLVAY brought this product onto the market at the beginning of 1996 as, in September 1995, the European Commission for Pharmaceutical Products in Brussels (CPMP) established that HFC 227 was suitable for pharmaceutical inhalers.
Dilution of the concentrated solution of carbonated magnesium di-n-propylate is carried out with the chosen HFC, preferably HFC 227, in pressurized containers, up to de-acidification reagent concentrations [carbonated magnesium di-n-propylate] lying between 1% and 10% (W/V), preferably between 1% and 10% (W/V) and up to concentrations of n-propanol less than 10% (V/V). In a particular and preferred embodiment of the invention, the product of the invention contains between 3.8 and 4.5% (W/V) of carbonated magnesium di-n-propylate, between 2 and 3% (V/V) of n-propanol, the rest of the mixture consisting of the HFC diluent chosen from HFC 227 and HFC 134a, and the product of the invention of said formulation is especially suitable for use with spray systems.
Additionally and optionally, the product of the invention may contain an inert gas, for example, nitrogen, with a view to achieving additional pressure and propulsion.
The resulting diluted solutions of carbonated magnesium di-n-propylate may be applied by conventional methods, for example, by direct spray onto the cellulose-type material. This method of applying the de-acidification product does not require prior desiccation, under vacuum, of the cellulose-type material, as the distribution and impregnation attained using the spray is very uniform and does not lead to the accumulation of any type of deposit or residue on the cellulose-type material to be treated. In general, it is advisable to work in a fume cupboard and use means of personal protection to avoid inhaling the spray.
The product of de-acidification product of the cellulose-type material can also be carried out by means of dissolving in HFC to a known concentration, for the bulk de-acidification of books and documents, using the equipment and method described in the Spanish patent application P9600016 filed by the same applicant. The apparatus described is formed of a treatment chamber, which serves for the drying stages under vacuum prior to impregnation and recovery of solvent by evaporation-condensation.
Therefore, the invention also provides a method for de-acidification of cellulose-type material, which comprises the application, of a quantity sufficient of the product of the invention for de-acidifying the cellulose-type material to be treated. The product of the invention may be applied to the cellulose-type material to be treated by means of a bulk de-acidification system or by spray.
The product of the invention can be obtained through a procedure that comprises:
preparing a solution of carbonated magnesium di-n-propylate in n-propanol; and
diluting said solution by addition of an HFC diluent selected from among HFC 134a and HFC 227.
In a particular embodiment, the concentration of carbonated magnesium di-n-propylate in said alcoholic solution lies between 30% and 70% (W/V).
Additionally and optionally, the product of the invention may contain an inert gas, for example, nitrogen.